Method of producing a roughening-treated copper foil

ABSTRACT

A roughening-treated copper foil, comprising (A) a copper foil, (B) a composite metal layer, which is formed on a bonding surface of the copper foil and comprises (I) copper, (II) at least one metal selected from the group consisting of tungsten and molybdenum and (III) at least one metal selected from the group consisting of nickel, cobalt, iron and zinc, and (C) a roughened layer comprising copper, which is formed on the composite metal layer.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a roughening-treated copper foiluseful for printed wiring boards or the like and to the productionthereof, particularly, to a roughening-treated copper foil, which isuseful for printed wiring boards due to its excellent adhesive strengthto resin base materials of high Tg's, such as FR-5, and to a methodsuitable for the production thereof.

[0003] (b) Description of the Related Art

[0004] Copper foil for printed wiring boards generally has a bondingsurface, which is previously roughened by some means to give higheradhesive strength on lamination onto resin base materials. Forelectrolytic copper foil, plating methods are mainly used as theroughening treatment. Japanese Patent Application Examined PublicationNo. 53-39376 (1978) discloses an example of the plating methods.According to the method, first a dendritic copper electrodepositionlayer is formed on at least one bonding surface of a copper foil as acathode by the so-called burning plating in an acidic copper platingbath at a current of the limiting current density or higher, then asmooth copper electrodeposition layer is formed on the dendritic copperelectrodeposition layer at a current of a current density lower than thelimiting current density (covering plating) to change the dendriticcopper into nodular copper and to increase the adhesive strength by thenodular copper. After the formation of the nodular copper by theelectrolysis treatment, the surface of the copper foil has a largerspecific surface than before the electrolysis treatment, and the nodularcopper works as an anchor, improving the adhesive strength between resinbase materials and the copper foil. When nodular copper is formed onelectrolytic copper foil, which generally has a surface (mat surface)rougher than the other surface (shiny surface), current is mainlycentered to convexes, and the formation of the nodular copper iscentered on the extreme ends of the convexes.

[0005] The recent spread of note type personal computers and pockettelephones has increased the use of glass-epoxy printed wiring boardsproduced by using as resin base materials FR-5 materials having highTg's. As compared with conventional FR-4 materials, epoxy resins havinghigh Tg's are more resistive to heat but have lower adhesive strength tocopper foil. A means of enhancing the adhesive strength of copper foilto resin base materials is to increase the roughness of the bondingsurface of copper foil. However, increasing the surface roughness tendsto cause the so-called copper powder-falling off that is the falling ofnodular copper even with small abrasion force and the so-called residualcopper that is nodular copper left in resin base materials after theetching step in the production of printed circuits.

[0006] Japanese Patent Application Examined Publication No. 54-38053(1979) discloses an improved method of forming a roughened surface bycarrying out electrolysis treatment at an approximate limiting currentdensity in an acidic copper plating bath to which a specific amount ofat least one metal selected from arsenic, antimony, bismuth, seleniumand tellurium is added. The addition of a very small amount of arsenic,antimony, bismuth, selenium or tellurium permits the formation of minuteprojections, but cannot solve the problem centering to the convexes onthe copper foil. Further, using copper foil containing arsenic,antimony, bismuth, selenium or tellurium, which are poisons or deadlypoisons, in printed wiring boards causes the problem of environmentalpollution on discarding etching waste liquors or the printed wiringboards.

[0007] Addition of benzoquinoline to an acidic copper plating bath(Japanese Patent Application Examined Publication No. 56-41196 (1981))or addition of molybdenum (Japanese Patent Application ExaminedPublication No. 62-56677 (1987)) are also proposed, but cannot improveadhesive strength sufficiently.

[0008] Japanese patent Application Unexamined Publication No. 8-236930(1996) discloses a method for solving the problem, wherein electrolysisis carried out at approximate limiting current density in an acidiccopper plating bath containing metal ions of at least one metal selectedfrom chromium and tungsten and metal ions of at least one metal selectedfrom vanadium, nickel, iron, cobalt, zinc, germanium and molybdenum, toform a roughening-treated layer containing the metals added. JapanesePatent Application Unexamined Publication No. 11-256389 (1999) disclosesa method of carrying out electrolysis at approximate limiting currentdensity in an acidic copper plating bath containing molybdenum ions andmetal ions of at least one metal selected from iron, cobalt, nickel andtungsten, to form a layer of burnt deposits (a layer formed by burningplating) containing the metals added.

[0009] These methods, however, also cause the phenomena of copperpowder-falling off and residual copper because nodular copper is formedexclusively on the extreme ends of the convexes on copper foil.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to solve the problems inthe prior arts. That is, an object of the present invention is toprovide a roughening-treated copper foil, which is suitable for printedwiring boards due to its high adhesive strength to resin base materials,by treating the bonding surface of copper foil by electrolysis so as toform nodular copper not only on the convexes on the bonding surface butalso on the concaves thereon without increasing the surface roughness.

[0011] Another object of the present invention is to provide a methodsuitable for producing the roughening-treated copper foil.

[0012] Accordingly, the present invention provides a roughening-treatedcopper foil, comprising

[0013] (A) a copper foil,

[0014] (B) a composite metal layer, which is formed on a bonding surfaceof the copper foil and comprises (I) copper, (II) at least one metalselected from the group consisting of tungsten and molybdenum and (III)at least one metal selected from the group consisting of nickel, cobalt,iron and zinc, and

[0015] (C) a roughened layer comprising copper, which is formed on thecomposite metal layer.

[0016] Herein, the terms “the bonding surface of a copper foil” mean asurface of a copper foil, which faces an adherent when the copper foilis bonded to the adherent.

[0017] The present invention further provides a method of producing aroughening-treated copper foil, comprising

[0018] treating a copper foil as a cathode by electrolysis in a platingbath containing (i) copper ions, (ii) metal ions of at least one metalselected from the group consisting of tungsten and molybdenum and (iii)metal ions of at least one metal selected from the group consisting ofnickel, cobalt, iron and zinc, at a current density lower than alimiting current density of the plating bath, to form on the copper foila composite metal layer comprising (I) copper, (II) at least one metalselected from the group consisting of tungsten and molybdenum and (III)at least one metal selected from the group consisting of nickel, cobalt,iron and zinc; and

[0019] forming a roughened layer comprising copper on the compositemetal layer by carrying out electrolysis in a plating bath containingcopper ions at a current density not lower than a limiting currentdensity of the plating bath to form a dendritic copper electrodepositionlayer, and then carrying out subsequent electrolysis at a currentdensity lower than the limiting current density of the plating bath toform nodular copper. Herein, the terms “the limiting current density ofthe plating bath” mean a current density at which generation of hydrogenaccompanies the cathode reaction for the deposition of the metals ormetal compounds.

BRIEF DESCRIPTION OF THE DRAWING

[0020]FIG. 1 is a scanning electron microscope photograph showing theroughened surface of the roughening-treated copper foil obtained inExample 1.

[0021]FIG. 2 is a scanning electron microscope photograph showing theroughened surface of the roughening-treated copper foil obtained inComparative Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A preferred example of the copper foil (raw copper foil) to beused in the present invention is electrolytic copper foil. It is alsopossible to use other ones, such as rolled copper foil or plastic filmcoated with copper film by, for example, vacuum plating. There is noparticular limitation in the thickness of the copper foil and theroughness and form of the surfaces of the copper foil. The copper foilmay have one or two bonding surfaces.

[0023] The bonding surface of the copper foil is coated with a compositemetal layer, which comprises (I) preferably 5,000 to 10,000 μg/dm² ofcopper, (II) preferably 10 to 1,000 μg/dm², more preferably 100 to 1,000μg/dm² of at least one metal selected from the group consisting oftungsten and molybdenum and (III) preferably 10 to 1,000 μg/dm², morepreferably 10 to 300 μg/dm² of at least one metal selected from thegroup consisting of nickel, cobalt, iron and zinc, all in coatingamount.

[0024] If the coating amount of the at least one metal selected from thegroup consisting of nickel, cobalt, iron and zinc is less than 10μg/dm², the formation of the nodular copper by the plating may notextend to the concaves on the copper foil, but be centered to theconvexes, and if more than 1,000 μg/dm², etching the plated layer mayrequire very long time to remove unnecessary copper to form coppercircuits. The coating amount of the at least one metal selected from thegroup consisting of nickel, cobalt, iron and zinc depends on thecomposition of the plating bath and the treating conditions, which maybe selected from those described later.

[0025] If the coating amount of copper in the composite metal layer isless than 5,000 μg/dm², the nodular copper may not be formed on theentire concaves, and if more than 10,000 μg/dm², the formation of thenodular copper on the entire concaves may be less effective and theproduction cost may increase. If the coating amount of the at least onemetal selected from the group consisting of tungsten and molybdenum inthe composite metal layer is less than 10 μg/dm², nodular copper may notbe formed on the entire concaves, and if more than 1,000 μg/dm², thenodular copper may not grow large. The composite metal layer ispreferably 0.05 to 0.15 μm thick, more preferably 0.07 to 0.12 μm thick.

[0026] According to the present invention, the composite metal layer isformed by treating the bonding surface of a copper foil as a cathode byelectrolysis in a plating bath containing (i) copper ions, (ii) metalions of at least one metal selected from the group consisting oftungsten and molybdenum and (iii) metal ions of at least one metalselected from the group consisting of nickel, cobalt, iron and zinc, ata current density lower than the limiting current density of the platingbath. The bonding surface of the copper foil is preferably subjected topickling and degreasing prior to the electrolysis.

[0027] The sources of the metal ions in the plating bath arewater-soluble metal salts. The following is a non-limitative butpreferred range of the composition of the bath.

[0028] copper ion source—copper sulfate pentahydrate: 10-100 g/l

[0029] tungsten ion source—sodium tungstate dehydrate: 0.01-20 g/l

[0030] molybdenum ion source—sodium molybdate dehydrate: 0.5-20 g/l

[0031] nickel ion source—nickel sulfate hexahydrate

[0032] cobalt ion source—cobalt sulfate heptahydrate

[0033] iron ion source—ferrous sulfate heptahydrate

[0034] zinc ion source—zinc sulfate heptahydrate

[0035] the total of nickel sulfate hexahydrate, cobalt sulfateheptahydrate, ferrous sulfate heptahydrate and zinc sulfateheptahydrate: 10-100 g/l

[0036] So far as the current density is lower than the limiting currentdensity of the plating bath, the electrolysis conditions are notlimited, and are generally selected from the following ranges.

[0037] current density: 1-10 A/dm²

[0038] electrolysis treatment period: 1-30 sec.

[0039] bath temperature: 10-60° C.

[0040] The preferred pH of the plating bath ranges from 1.5 to 5.0. Ifthe pH is lower than 1.5, the preferred ranges of the coating amounts ofthe at least one metal selected from the group consisting of tungstenand molybdenum and the at least one metal selected from the groupconsisting of nickel, cobalt, iron and zinc in the composite layer maybe narrowed, so that the formation of nodular copper by the plating doesnot extend to the concaves on the copper foil but be centered on theconvexes. If the pH is higher than 5.0, it may take a very long time todissolve the metal ions of at least one metal selected from tungsten andmolybdenum, lowering the productivity. The pH more preferably rangesfrom 2.0 to 4.0.

[0041] By forming the composite metal layer, fine particles are formedon the convexes on the copper foil, but cannot give sufficient adhesivestrength as they are or even after coated with copper by burning platingor covering plating. To improve adhesive strength, a roughened layercomprising copper is formed on the composite metal layer by using bothburning plating and covering plating to deposit nodular copper furtheron the concaves on the copper foil.

[0042] That is, the copper foil treated under the above-describedconditions is washed with water, and then a roughened layer comprisingcopper is formed on the composite metal layer by carrying out burningplating whereby a dendritic copper electrodeposition layer is formed byelectrolysis in a plating bath containing copper ions at a currentdensity not lower than the limiting current density of the plating bath,followed by covering plating whereby nodular copper is formed byelectrolysis at a current density lower than the limiting currentdensity of the plating bath.

[0043] The coating amount of copper in the roughened layer comprisingcopper is preferably 30,000 to 300,000 μg/dm². If it is less than 30,000μg/dm², copper nodules may be too small to give sufficient adhesivestrength, and if more than 300,000 μg/dm², adhesive strength may besufficient, but the production cost will be problematically high. Morepreferred coating amount is 100,000 to 200,000 μg/dm². The combined stepof burning plating/covering plating may be repeated to form theroughened layer comprising copper.

[0044] In cases where the roughened layer comprising copper is formed byusing a common sulfuric acid-acidic copper sulfate bath, preferred butnon-limitative examples of the composition of the bath and electrolysisconditions are as follows.

[0045] copper ion source—copper sulfate pentahydrate: 20-300 g/l

[0046] sulfuric acid: 10-200 g/l

[0047] current density: burning plating (not lower than limiting currentdensity of the plating bath)—10-200 A/dm²; covering plating (lower thanlimiting current density or the plating bath)—1-20 A/dm²

[0048] electrolysis treatment period: burning plating—1-10 seconds;covering plating—40-100 seconds

[0049] bath temperature: 20-60° C.

[0050] On the copper foil coated with the roughened layer comprisingcopper, it is preferable to form other layers commonly formed on copperfoil, for example, a rust preventing layer, such as a chromate layer, azinc layer, a copper-zinc alloy layer, a zinc alloy layer, anickel-molybdenum-cobalt layer or an indium-zinc layer, a coupling agenttreatment layer, or an adhesive resin layer, such as a phenolic resin,epoxy resin or polyimide resin layer, according to demands. Theroughening-treated copper foil coated with the above-described layers islaminated onto a resin base material with heat and pressure, to form acopper-clad laminate for printed wiring boards.

[0051] Hereinafter the present invention will be described in moredetail referring to Examples and Comparative Examples, which, however,do not limit the scope of the present invention.

EXAMPLES 1 TO 8 AND COMPARATIVE EXAMPLES 1 TO 8 Example 1

[0052] (1) A 35 μm thick electrolytic copper foil (surface roughness Raof mat surface: 0.9 μm as measured according to JIS B 0601) wassubjected to pickling for 20 seconds by using a 10% sulfuric acidsolution.

[0053] (2) The copper foil was then washed with water, and the matsurface (bonding surface) of the copper foil was treated by electrolysisat a current density of 6 A/dm² for 4 seconds in a plating bath, whichcontained 50 g/l of copper sulfate pentahydrate, 2 g/l of sodiummolybdate dehydrate and 50 g/l of nickel sulfate hexahydrate and wasadjusted to pH 3.0 and to a bath temperature of 30° C., to form on thebonding surface of the copper foil a composite metal layer containingcopper molybdenum and nickel. The coating amounts of the metals in thecomposite metal layer were measured by an ICP (inductively coupledplasma luminescent) analyzer to be 7,900 μg/dm² of copper, 178 μg/dm² ofmolybdenum and 145 μg/dm² of nickel. After the treatment, the treatedsurface had a surface roughness Ra of 0.9 μm.

[0054] (3) The copper foil was then washed with water, and the surfaceof the composite metal layer was treated by {circle over (1)}electrolysis at a current density of 30 A/dm² (not lower than thelimiting current density) for 3 seconds followed by {circle over (2)}electrolysis at 5 A/dm² (lower than the limiting current density) for 80seconds both in a plating bath containing 130 g/l of copper sulfatepentahydrate and 100 g/l of sulfuric acid and adjusted to a bathtemperature of 30° C., to form a roughened layer comprising copper. Theroughened layer comprising copper had a coating amount of copper of150,000 μg/dm² and a surface roughness Ra of 1.4 μm. On theroughening-treated electrolytic copper foil was observed nodular copperformed all over the irregularities on the copper foil. FIG. 1 shows ascanning electron microscope photograph (magnification: 2000, objectangle: 45°) of the roughened surface.

[0055] (4) The copper foil was then washed with water, and dipped for 10seconds in an aqueous solution of 3.5 g/l of sodium bichromate dihydrateadjusted to pH 4.2 and a bath temperature of 28° C., to form a rustpreventing layer.

[0056] (5) The copper foil was then washed with water, dipped for 10seconds in an aqueous solution of 0.1 wt %3-glycidoxypropyltrimethoxysilane, and then immediately dried at 80° C.,to form a silane coupling agent treatment layer. form on the bondingsurface of the copper foil a composite metal layer containing copper,molybdenum, cobalt and iron. The coating amounts of the metals in thecomposite metal layer were measured by an ICP (inductively coupledplasma luminescent) analyzer to be 7,900 μg/dm² of copper, 180 μg/dm² ofmolybdenum, 12 μg/dm² of cobalt and 50 μg/dm² of iron. After thetreatment, the treated surface had a surface roughness Ra of 0.9 μm.Subsequently, a roughened layer comprising copper was formed in the samemanner as in Example 1. The roughened layer comprising copper had acoating amount of copper of 150,000 μg/dm² and a surface roughness Ra of1.5 μm. On the roughening-treated electrolytic copper foil was observednodular copper formed all over the irregularities on the copper foil.

[0057] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Example 3

[0058] After the same electrolytic copper foil as that used in Example 1was pickled and washed with water in the same manner as in Example 1,the mat surface (bonding surface) of the copper foil was treated byelectrolysis at a current density of 7 A/dm² for 4 seconds in a platingbath, which contained 50 g/l of copper sulfate pentahydrate, 2 g/l ofsodium molybdate dehydrate and 50 g/l of zinc sulfate heptahydrate andwas adjusted to pH 2.5 and to a bath temperature of 30° C., to form onthe bonding surface of the copper foil a composite metal layercontaining copper, molybdenum and zinc. The coating amounts of themetals in the composite metal layer were measured by an ICP (inductivelycoupled plasma luminescent) analyzer to be 9,200 μg/dm² of copper, 230μg/dm² of molybdenum and 159 μg/dm² of m. On the roughening-treatedelectrolytic copper foil was observed nodular copper formed all over theirregularities on the copper foil.

[0059] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Example 5

[0060] After the same electrolytic copper foil as that used in Example 1was pickled and washed with water in the same manner as in Example 1,the mat surface (bonding surface) of the copper foil was treated byelectrolysis at a current density of 6 A/dm² for 4 seconds in a platingbath, which contained 50 g/l of copper sulfate pentahydrate, 10 g/l ofsodium tungstate dihydrate, 30 g/l of cobalt sulfate heptahydrate and 30g/l of ferrous sulfate heptahydrate and was adjusted to pH 2.0 and to abath temperature of 30° C., to form on the bonding surface of the copperfoil a composite metal layer containing copper, tungsten, cobalt andiron. The coating amounts of the metals in the composite metal layerwere measured by an ICP (inductively coupled plasma luminescent)analyzer to be 7,900 μg/dm² of copper, 200 μg/dm² of tungsten, 12 μg/dm²of cobalt and 50 μg/dm² of iron. After the treatment, the treatedsurface had a surface roughness Ra of 0.9 μm. Subsequently, a roughenedlayer comprising copper was formed in the same manner as in Example 1.The roughened layer had a surface roughness Ra of 1.5 μm. On theroughening-treated electrolytic copper foil was observed nodular copperformed all over the irregularities on the copper foil.

[0061] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Example 6

[0062] After the same electrolytic copper foil as that used in Example 1was pickled and washed with water in the same manner as in Example 1,the mat surface (bonding surface) of the copper foil was treated byelectrolysis at a current density of 7 A/dm² for 4 seconds in a platingbath, which contained 50 g/l of copper sulfate pentahydrate, 1 g/l ofsodium tungstate dihydrate, 2 g/l of sodium molybdate dihydrate and 50g/l of zinc sulfate heptahydrate and was adjusted to pH 2.5 and to abath temperature of 30° C., to form on the bonding surface of the copperfoil a composite metal layer containing copper, tungsten, molybdenum andzinc. The coating amounts of the metals in the composite metal layerwere measured by an ICP (inductively coupled plasma luminescent)analyzer to be 9,200 μg/dm² of copper, 50 μg/dm² of tungsten, 180 μg/dm²of molybdenum and 160 μg/dm² of zinc. After the treatment, the treatedsurface had a surface roughness Ra of 0.9 μm. Subsequently, a roughenedlayer comprising copper was formed in the same manner as in Example 1.The roughened layer comprising copper had a surface roughness Ra of 1.4μm. On the roughening-treated electrolytic copper foil was observednodular copper formed all over the irregularities on the copper foil.

[0063] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Example 7

[0064] The same treatments as in Example 4 were repeated except that a18 μm thick rolled copper foil (surface roughness Ra: 0.1 μm) was used,to form a composite metal layer containing copper, tungsten and nickel.The coating amounts of the metals in the composite metal layer were7,900 μg/dm² of copper, 145 μg/dm² of tungsten and 128 μg/dm² of nickel.After the treatment, the treated surface had a surface roughness Ra of0.1 μm. Subsequently, a roughened layer comprising copper was formed inthe same manner as in Example 1. The roughened layer comprising copperhad a surface roughness Ra of 0.5 μm.

[0065] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Example 8

[0066] The same treatments as in Example 4 were repeated except that a12 μm thick electrolytic copper foil (surface roughness Ra of the matsurface: 0.2 μm) was used, to form a composite metal layer containingcopper, tungsten and nickel. The coating amounts of the metals in thecomposite metal layer were 7,900 μg/dm² of copper, 150 μg/dm² oftungsten and 135 μg/dm² of nickel. After the treatment, the treatedsurface had a surface roughness Ra of 0.2 μm. Subsequently, a roughenedlayer comprising copper was formed in the same manner as in Example 1.The roughened layer comprising copper had a surface roughness Ra of 0.6μm.

[0067] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Comparative Example 1

[0068] The same treatments as in Example 1 were repeated except that thestep (3) for forming a roughened layer by using a with water and thentreated by electrolysis at a current density of 5 A/dm² (lower than thelimiting current density) for 80 seconds by using a plating bath, whichcontained 130 g/l of copper sulfate pentahydrate and 100 g/l of sulfuricacid and was adjusted to a bath temperature of 30° C., to form a smoothcopper layer (covering plating). The smooth copper layer had a coatingamount of copper of 132,000 μg/dm² and a surface roughness Ra of 1.1 μm.

[0069] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Comparative Example 5

[0070] The same electrolytic copper foil as that used in Example 1 waspickled and washed with water in the same manner as in Example 1.Without forming a composite metal layer, the mat surface (bondingsurface) of the copper foil was then treated in a plating bath of a bathtemperature of 30° C. containing 130 g/l of copper sulfate pentahydrateand 100 g/l of sulfuric acid by {circle over (1)} electrolysis at acurrent density of 30 A/dm² (not lower than the limiting currentdensity) for 3 seconds and {circle over (2)} electrolysis at a currentdensity of 5 A/dm² (lower than the limiting current density) for 80seconds, to form a roughened layer comprising copper. The roughenedlayer comprising copper had a coating amount of copper of 150,000 μg/dm²and a surface roughness Ra of 1.8 μm. On the roughening-treatedelectrolytic copper foil was observed the formation of nodular coppercentered on the convexes on the irregular surface of the copper foil.FIG. 2 shows a scanning electron microscope photograph (magnification:2000, object angle: 45°) of the roughened surface.

[0071] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Comparative Example 6

[0072] The same rolled copper foil as that used in Example 7 was pickledand washed with water in the same manner as in Example 1. Withoutforming a composite metal layer, the mat surface (bonding surface) ofthe copper foil was then treated in a plating bath of a bath temperatureof 30° C. containing 130 g/l of copper sulfate pentahydrate and 100 g/lof sulfuric acid by {circle over (1)} electrolysis at a current densityof 30 A/dm² (not lower than the limiting current density) for 3 secondsand {circle over (2)} electrolysis at a current density of 5 A/dm²(lower than the limiting current density) for 80 seconds, to form aroughened layer comprising copper. The roughened layer comprising copperhad a coating amount of copper of 150,000 μg/dm² and a surface roughnessRa of 0.8 μm.

[0073] After the treatments (4) and (5) of Example 1 were carried out,the measurement of adhesive strength and tests for residual copper andpowder falling were carried out in the same manner as in Example 1 (6),and the results are listed in Table 1.

Comparative Example 7

[0074] The same electrolytic copper foil as that used in Example 8 waspickled and washed with water in the same manner as in Example 1.Without forming a composite metal layer, the mat surface (bondingsurface) of the copper foil was then treated in a plating bath of a bathtemperature of 30° C. containing 130 g/l of copper sulfate pentahydrateand 100 g/l of sulfuric acid by {circle over (1)} electrolysis at acurrent density of 30 A/dm² (not lower than the limiting currentdensity) for 3 seconds and {circle over (2)} electrolysis at a currentdensity of 5 A/dm² (lower than the limiting current density) TABLE 1Adhesive strength kN/m Residual copper Powder-falling Example 1 2.0 NoNo Example 2 1.9 No No Example 3 1.9 No No Example 4 2.0 No No Example 52.1 No No Example 6 1.9 No No Example 7 1.0 No No Example 8 0.9 No NoComp. 0.9 No Countless particles Example 1 of about 0.1 μm in diameterComp. 0.9 No Countless particles Example 2 of about 0.1 μm in diameterComp. 1.0 No Countless particles Example 3 of about 0.1 μm in diameterComp. 1.3 No No Example 4 Comp. 1.6 15 particles of 10 μm 23 particlesof 2-10 Example 5 or less in diameter μm in diameter Comp. 0.5 8particles of 10 μm 15 particles of 2-10 Example 6 or less in diameter μmin diameter Comp. 0.5 7 particles of 10 μm 18 particles of 2-10 Example7 or less in diameter μm in diameter Comp. 1.7 2 particles of 10 μm 3particles of 2-10 Example 8 or less in diameter μm in diameter

[0075] As apparent from comparison of FIG. 1 with FIG. 2, unlike theroughening-treated copper foil obtained in Comparative Example 5 onwhich nodular copper was locally electrodeposited on the convexes on thecopper foil surface,

What is claimed is,
 1. A roughening-treated copper foil, comprising (A)a copper foil, (B) a composite metal layer, which is formed on a bondingsurface of the copper foil and comprises (I) copper, (II) at least onemetal selected from the group consisting of tungsten and molybdenum and(III) at least one metal selected from the group consisting of nickel,cobalt, iron and zinc, and (C) a roughened layer comprising copper,which is formed on the composite metal layer.
 2. The roughening-treatedcopper foil of claim 1, wherein the composite metal layer comprises5,000 to 10,000 μg/dm² of copper, 10 to 1,000 μg/dm² of at least onemetal selected from the group consisting of tungsten and molybdenum and10 to 1,000 μg/dm² of at least one metal selected from the groupconsisting of nickel, cobalt, iron and zinc, all in coating amount. 3.The roughening-treated copper foil of claim 1, wherein the roughenedlayer comprises 30,000 to 300,000 μg/dm² of copper in coating amount. 4.The roughening-treated copper foil of claim 2, wherein the roughenedlayer comprises 30,000 to 300,000 μg/dm² of copper in coating amount. 5.A method of producing a roughening-treated copper foil, comprisingtreating a copper foil as a cathode by electrolysis in a plating bathcontaining (i) copper ions, (ii) metal ions of at least one metalselected from the group consisting of tungsten and molybdenum and (iii)metal ions of at least one metal selected from the group consisting ofnickel, cobalt, iron and zinc, at a current density lower than alimiting current density of the plating bath, to form on the copper foila composite metal layer comprising (I) copper, (II) at least one metalselected from the group consisting of tungsten and molybdenum and (III)at least one metal selected from the group consisting of nickel, cobalt,iron and zinc; and forming a roughened layer comprising copper on thecomposite metal layer by carrying out electrolysis in a plating bathcontaining copper ions at a current density not lower than a limitingcurrent density of the plating bath to form a dendritic copperelectrodeposition layer and then carrying out subsequent electrolysis ata current density lower than the limiting current density of platingbath to form nodular copper.
 6. The method of claim 5, wherein theplating bath containing (i) copper ions, (ii) metal ions of at least onemetal selected from the group consisting of tungsten and molybdenum and(iii) metal ions of at least one metal selected from the groupconsisting of nickel, cobalt, iron and zinc is pH 1.5 to 5.0.